Over the last decade, the optical fibers have been developed and installed as the backbone of interoffice networks for voice, video and data transmission. These are becoming important with growing and expanding telecommunication infrastructure. Their importance is further increasing because of their high bandwidth applicability. The higher bandwidth demand is further increasing exponentially with time because of rapid growth of information technology.
The capacity of lightwave communication systems has undergone enormous growth during the last decade. The growing bandwidth demand can be met by using a dense wavelength division multiplexing, hereinafter referred to as DWDM, approach with low dispersion fibers. The requirements of fiber have had to change to support these advances, especially the requirement for the amount and uniformity (slope) of chromatic dispersion across these wavelengths. The DWDM approach enhances the effective data rate of an optical fiber link by, increasing the number of wavelength channels within the wavelength band.
Conventionally, the multi-mode fiber at wavelength of 850 nm were used, which were replaced by single mode fibers with zero dispersion wavelength near 1310 nm. The single mode or monomode optical fibers have greater bandwidth than that of the multimode fibers.
Therefore, the research has been directed towards the development of the single mode fibers, as these fibers were observed to have lower attenuation between the wavelength range from 1300 nm to 1550 nm.
However, when single wavelength moved through 1550 nm window for lower attenuation, the single mode fibers were observed to have very high dispersion.
The major disadvantage of the single mode fibers with high dispersion at 1550 nm was that, it obstructed higher bit rate transmission. This disadvantage of single mode fibers has been overcome by the improved single mode fibers, known as dispersion shifted fibers, which have zero dispersion even when the wavelength shifted to 1550 nm.
The theoretical analysis reveals that a single mode fiber having Low dispersion and low dispersion slope with higher effective area is most desirable for high capacity DWDM, as referred hereinabove, transmission. However, the dispersion shifted fibers used for long distance systems in the prior art have higher dispersion which promotes poor DWDM performance. The dispersion flattened fiber which specify the dispersion magnitude less than 2 ps/nm.km between 1.3 to 1.6 μm have zero dispersion region within the DWDM window. This result is strong four wave mixing, which prevents good DWDM performance.
Ideally the dispersion of an optical fiber should have a constant value over the entire wavelength-operating region. However, the dispersion of fibers varies with the wavelength as the refractive index varies with the wavelength. Their dispersion slope S0 quantifies this variability. The smaller the slope the less the dispersion varies with the wavelength. Another advantage of the low dispersion and low dispersion slope fiber is that its small dispersion allows its minimum dispersion to be increased to better suppress the Four Wave Mixing non-linearity, while still keeping the fiber minimum dispersion small enough for the signals to travel to longer distances with minimum need for dispersion and dispersion slope compensation.
The prior art of the chromatic dispersion fiber has been illustrated in FIG. 1. It is a result of material and the waveguide dispersion. In the theoretical treatments of intramodal dispersion it is assumed, for simplicity, that the material and the waveguide dispersion can be calculated separately and then added to give the total dispersion of the mode. In reality these two mechanisms are intrinsically related, since the dispersive properties of the refractive index, which gives rise to material dispersion, also affect the waveguide dispersion. Material dispersion occurs because the index refraction varies as a function of the optical wavelength. On the other way waveguide dispersion is a function of the refractive index profile shape.
The parameters, like refractive index and radius of each part of the fibre, like centre core, cladding(s), ring core(s) and outer core, and the relationship between refractive index and radius of such parts of the fibre, and number of cores and claddings decide the characteristic properties of thus obtained fiber and the applications of thus obtained fiber.
Therefore, the fibers known in the art are distinguished by way of their characteristic properties, which in-turn are decided by various parameters as stated herein above. The fibers as known in the prior art either have low non-linearity but high bend loss or have low bend loss but less effective area or may have higher non-linearity and higher bend loss or may have non-uniform chromatic dispersion over the third and fourth window or high dispersion slope, that is the fibre will not have optimum characteristic properties and will sacrifice one of the property for achieving another property.
It has been observed that the dispersion and dispersion slope varies with the wavelength and refractive index varies with the wavelength.
Therefore, in view of variation of dispersion and dispersion slope with the wavelength and variation of refractive index with the wavelength constant efforts are being made to develop optical fibers which have optimum dispersion and dispersion slope and yet having such a refractive index profile and the configuration which is easy to be achieved and accordingly it is easy to fabricate the desired fiber which is suitable in as wider range of the wavelength as possible.
Therefore, the inventors of the present invention have made an attempt to develop the fiber, which will have optimum characteristic properties, that is which will not sacrifice one of the characteristic property to achieve another characteristic property.